The invention relates to a method for determining and automatically correcting horizontal and vertical errors in image steadiness during television image scanning of continuously moving motion picture film having a succession of image frames. More particularly, the invention relates to a method of the type disclosed in U.S. Pat. No. 4,903,131, which issued on Feb. 20, 1990. The disclosure of that patent is incorporated herein by reference.
U.S. Pat. No. 4,903,131 discloses a method in which video signals produced during image scanning are temporarily stored in an image buffer memory. Vertical image steadiness error signals are used to determine the start of scanning of the first television scan line for each film frame, as well as the start of writing the video signals for the film frame into memory, in dependence upon the vertical position of a film frame relative to the television image scanner. Standard television horizontal and vertical timing pulses are produced in synchronism with studio timing pulses, and video signals are read out of the memory in dependence upon the standard pulse.
Frame start pulses produced from the vertical error signals are released only during a portion of the scanning period, and are blocked during the remainder of the period. The blocking and releasing in each scanning period are determined by a tachometer roll such as a sprocket which engages perforations in the film without slippage. Substitute pulses derived from the tachometer are automatically provided during the release period if frame start pulses are missing.
U.S. Pat. No. 4,903,131 describes the recovery of image frame start pulses and horizontal position values for correcting vertical and horizontal errors in image steadiness. It does not provide a detailed discussion of how vertical and horizontal correction values, respectively, are supplied in case of failure or incorrect position of the frame start pulses and the horizontal position values, respectively.